Sort results in descending order within days.

Fixes #24.
Update Crossfilter.
Upgrade to D3 version 3.
Update to Crossfilter v1.2.0.
Fix date dimension.

The date dimension was originally defined on a per-day basis, using
d3.time.day.  This resulted in date.top(40) returning the top 40 flights
when ordered by day, but within a day, the flights were not necessarily
ordered by time.

The fix is to define the date dimension using the full date and time,
and then define the group using d3.time.day instead.

Fixes #77, #24.
Update Crossfilter.
Update D3.
Update Crossfilter.
Update Crossfilter.
Update D3.
Update Crossfilter.
Update Crossfilter.
Update Crossfilter.
Update Crossfilter.
DJR:Added Twitter Bootstrap for multi-column display
Update Crossfilter.
Update Crossfilter.
Merge recent changes

Merge remote-tracking branch 'github/gh-pages' into gh-pages

* github/gh-pages:
  Update Crossfilter.
  Update Crossfilter.
cleanup of bootstrap multi-column display branch

I like the two column idea in #108. I've cleaned up that branch
to remove superfluous whitespace changes which should make
review easier. I also simplified this commit by removing the
button attributes on the links, and separately recovered
some of the margin.